High molecular weight (for example, Mw greater than 150,000 g/mole) ethylene/α-olefin/non-conjugated polyene interpolymers (for example, EPDM terpolymers) with low levels of long chain branching (LCB), as indicated by rheology features (for example, tan delta, V0.1, V100), are useful in many applications, such as TPVs (Thermoplastic Vulcanizates) and high filler compounds. However, production of such high molecular weight interpolymers, in a solution process, has been challenging, for two main reasons: a) the difficulties associated with transporting a high viscosity molten polymer through, and out of, the solution reactors, and b) the need for a catalyst which can produce such high molecular weight interpolymers at commercially viable operating conditions. Thus, there is a need for new polymerization processes to form high molecular weight ethylene/α-olefin/non-conjugated polyene interpolymers with low levels of long chain branching (LCB). This need has been met by the following invention.